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The Garden Plot for August 24, 2007
3:55 PM - 4:00 PM
[Program Website]
Today's Highlight: “Tree Care II”
How are you treating your trees this summer? People who come into the Extension Office are surprised that I can tell them exactly the year they forgot to water, or put in a new driveway, just by looking at their tree’s branches and twigs. Trees maintain a living record of how well we care for them. This year’s branches tell me about past year’s twig growth. If annual twig growth is less than 2-3 inches per year, something may be restricting your tree’s growth. That’s when you need to become a plant detective and figure out just what your trees are telling you. Here are some things your trees may be saying by the way they grow:
Lack of water results in yellow and/or brown leaf margins. Lack of water may be the greatest limiting factor to tree growth. Discolored leaf margins can also mean tree roots have been injured by construction or soil compaction.
Trees have species-specific light requirements; too little or too much can decrease overall growth, change leaf color change, and cause leaf drop.
Poor leaf color can mean a lack of one or more plant nutrients. The most common nutrient deficiency we see on trees in Montana is lack of iron. Trees that evolved in lower pH, acid soils in the eastern US or in Europe often react to Montana’s higher pH soils with iron deficiency symptoms, such as yellowing between the veins of newest leaves. Older leaves stay greener.
Round or irregular dark spots on leaves with lighter colored “halos” surrounding them may mean fungus disease. Nine times out of ten, we can trace disease back to frequent irrigation with overhead sprinklers, or worse: sprinkler irrigation at night.
Distorted, curled and crinkled, yellow-white leaves may mean you got too close to tree roots with herbicide spray meant for the lawn.
What should we do if our trees give us a bad tree care report? Get back to the basics of good tree care, including:
PROPER SITE SELECTION Match the tree to the growing conditions. Choose trees hardy to your HARDINESS ZONE (generally 3- 4 in our area). Consider the tree’s water, light, soil, and pH preferences.
PRUNING The best time to prune is after the tree has gone dormant and before bud break. Never remove more than 30% of total tree height. To reduce height, cut back to a lateral branch that is at least one-half the diameter of the branch you are cutting.
WATERING Exotic shade trees require an average of 30 to 40 inches of precipitation per year. That means about 2 inches per week of added irrigation in Western Montana. Short, frequent irrigation may encourage shallow, surface roots. Water less frequently (every 7-10 days), depending on soil type, for one to several hours. The lighter the soil, the shorter the irrigation interval and frequency should be.
FERTILIZING Tree fertilizers should only be used to promote normal growth (4-6 inches of new growth per year). Never fertilize a stressed tree; it may cause the tree to use up its last food reserves and trigger early mortality. Don’t apply nitrogen fertilizer after the first week in July
FOR CURRENT INFORMATION ON INSECT AND DISEASE PESTS OF TREES CALL THE MISSOULA COUNTY PEST ALERT PHONE LINE AT 258-3820
Helen Atthowe's new short program of gardening tips
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